In certain oil reservoirs, the pressure inside the reservoir is insufficient to push wellbore fluids to the surface without the help of a pump or other so-called artificial lift technology such as gas lift in the well. With a gas-based artificial lift system, external gas is injected into special gas lift valves placed inside a well at specific design depths. The injected gas mixes with produced fluids from the reservoir, and the injected gas decreases the pressure gradient inside the well, from the point of gas injection up to the surface. Bottom hole fluid pressure is thereby reduced, which increases the pressure drawdown (pressure difference between the reservoir and the bottom of the well) to increase the well fluid flow rate.
Other artificial lift technologies may also be used, e.g., electro-submersible pumps (ESPs), progressing cavity pumps (PCPs), sucker rod pumps (SRPs), hydraulic jet pumps, hydraulic piston pumps. Furthermore, with some oil reservoirs, a mixture of artificial lift technologies may be used on different wells. In addition, other production optimization technologies may be used in some reservoirs, e.g., chemical stimulation using diluents, inhibitors, surfactants, etc. to increase the flow of wellbore fluids within such reservoirs. Given also that multiple wells coupled to the same reservoir may impact the production of one another, additional technologies, such as chokes and other flow restriction devices, may also be used in some wells to control well fluid flow rate. Further, combinations of these technologies may also be used in some wells. As such, a number of different technologies, referred to herein as well flow rate management technologies, may be used to control the well fluid flow rate of a well.
Specifically with respect to gas lift and artificial lift systems, during the initial design of a gas lift or other artificial lift system to be installed in a borehole, software models have traditionally been used to determine the best configuration of artificial lift mechanisms, e.g., the gas lift valves, in a well, based on knowledge about the reservoir, well and reservoir fluids. However, models that are limited to single wells generally do not take into account the effects of other wells in the same field, and it has been found that the coupling through the surface network of wells in the same field will affect the actual rates experienced by each well.
Software models have also been developed to attempt to optimally configure artificial lift mechanisms for multiple wells coupled to each other in the same oilfield or surface production network. Such models, which may be referred to as surface network models, better account for the interrelationships between wells and the artificial lift mechanisms employed by the various wells. Nonetheless, shortcomings still exist with such multi-well models. For example, a surface network model is an approximation to reality, so the computed optimized lift gas rates for a gas-based artificial lift system are an approximation to the true optimum rates. In addition, a surface network model generally has to be continually re-calibrated so that it remains an accurate representation of the real network. Online measurements of a surface production network (e.g., actual measurements of pressures, temperatures and flow rates) generally are cross-checked against model calculations to insure that the two are consistent. If they differ substantially, a human operator may intervene to alter the surface network model to improve the match. In addition, in some instances a surface network model may have to be re-run whenever surface network conditions change, that is, whenever the well head flowing back pressures change, so that optimized lift gas rate values change. Surface network conditions can change frequently, for example, in response to instantaneous changes in the surface facility settings, equipment status and availability (equipment turning on and off), changes in ambient temperature, and at slower time scales, changes in fluid composition such as gas-oil ratio and water cut and surface network solid buildup or bottle-necking.
Therefore, a need continues to exist in the art for an improved manner of optimizing artificial lift technologies and other well flow rate management technologies for multiple wells in a multi-well production network.